1. Field of the Invention
This invention relates to improved, high strength polyethylene yarns useful in ballistic-resistant, cut-resistant and other applications, fabrics produced from these yarns and the methods by which the yarns and fabrics are made.
2. Description of the Related Art
Among the requirements that protective clothing such as personal body armor, chain saw chaps, and others must meet, in addition to ballistic-resistance and/or cut resistance, are comfort and flexibility. Multiple layers of woven fabrics consisting of high strength and high modulus fibers are commonly used in such protective clothing.
The preparation of high strength, polyethylene filaments and/or multi-filament yarns has been described for example in U.S. Pat. Nos. 4,411,854, 4,413,110, 4,422,993, 4,430,383, 4,436,689, 4,455,273, 4,536,536, 4,545,950, 4,551,296, 4,584,347, 4,663,101, 5,248,471, 5,578,374, 5,736,244, 5,741,451, 5,972,498 and 6,448,359 B1. Ballistic-resistant articles prepared from such high strength polyethylene filaments have been described for example in U.S. Pat. Nos. 4,403,012, 4,457,985, 4,623,574, 4,650,710, 4,737,401, 4,737,402, 4,748,064, 4,883,700, 4,916,000, 5,061,545, 5,160,776, 5,167,876, 5,175,040, 5,187,023, 5,196,252, 5,343,796, 5,376,426, 5,440,965, 5,480,706, 5,677,029, 5,788,907, 5,804,015, 5,958,804, 6,003,424, and 6,276,254 B1.
U.S. Pat. No. 4,403,012 indicates that the fibers may be formed into a fabric by any of a variety of conventional techniques. U.S. Pat. No. 4,737,401 broadly indicates that plain woven, basket woven, satin and crow feet woven fabrics, etc., can be made from high strength polyethylene filaments. However, to efficiently use conventional weaving equipment, the yarns to be woven must have some minimum degree of yarn coherence to avoid snags and wild loops which effect fabric quality and may stop the loom. Weaving is also enhanced when the yarn to be woven is essentially round in cross-section and does not flatten when passing over guides. On the other hand, for maximum ballistic-effectiveness it is desirable that the yarns in woven fabrics are flat and are spread out into thin layers.
Methods to achieve yarn coherence have included twisting, jet entanglement, and application of sizing material. Twisting improves the roundness of yarn bundles but it is known that twisting reduces the ballistic effectiveness of fabrics produced from these yarns. This may be in part because twisting induces stress in the yarns and in part because twisting prevents the woven yarns from spreading into thin layers.
Air jet entanglement of yarn filaments as taught, for example, by U.S. Pat. No. 5,579,628, provides yarn coherence and improves ballistic-resistance as compared to twisted yarns. However, air jet entanglement may also damage the yarn and is an expensive process in both capital costs for air compressors and in operating costs for energy consumption.
Sizing of a plain weave fabric made from untwisted high strength polyethylene filaments with polyvinyl alcohol has previously been described in U.S. Pat. No. 4,737,401. A process that covered virtually all yarn surfaces of synthetic filament yarns with sizing has been described in U.S. Pat. No. 4,858,287.
Each of the methods and yarns cited above represented improvements in the state of their respective arts. Nevertheless, none described the specific constructions of the yarns and fabrics of this invention and the methods by which they are achieved.